Can we bypass the vbios/graphics within Coreboot and deliver the Linux kernel payload and use its graphics?
Yes, that would work. (In the case of Intel hardware) the Linux grap- phics driver does a superset of the things the VBIOS does. Actually, its default case is to ignore what the VBIOS did and start all over again. (One technical detail: You'd still have to put the Video BIOS Table, VBT into coreboot.)
As my very modest knowledge about vBIOS and Legacy BIOS is (I am, as we speak, trying to understand much more in-depth about differences between UEFI and Legacy), I think that, if you tend to bring Legacy based Coreboot, there is NO chance to avoid VBT (Video BIOS Table), which should/must be passed to Linux kernel, so Linux should/must reuse it for its own GFX (with much richer super set of functionality).
In contrary, if you use UEFI based context, then, instead of VBT you'll use so called GOP driver (The Graphics Output Protocol (GOP) is enabled by UEFI driver to support graphic console output in the pre-OS phase).
The ultimate goal of GOP is to replace legacy VGA BIOS and eliminate VGA HW functionality. Once you bring OS, it will NOT inherit GOP, rather use its own GFX from scratch (sans VBT).
My two cent to this thread, Zoran